The invention concerns power regulation in a radio system, such as a cellular radio system, in connection with radio links or in an ad-hoc network.
In a mobile communications system, regulation of the transmission power is performed in the mobile station MS and/or at the base transceiver station BTS in order to lower the network""s interference level and to compensate for fading on the radio path. Usually, the objective of power regulation is constantly to preserve the received signal almost at the same power level, which is as low as possible, however, in such a way that the quality of the received signal will not suffer. When the level and/or quality of the signal in the radio communication between the mobile communications network and the mobile station drops below the desired level, regulation of the transmission power may be carried out at the base transceiver station and/or in the mobile station MS in order to improve the radio communication. The transmission power of the mobile station MS is usually regulated from the fixed network with the aid of a special power regulation algorithm.
FIG. 1 in the appended drawing shows a simplified block diagram of the GSM system (Global System for Mobile communications). The mobile station MS is connected over the radio path with some base transceiver station BTS, which is base transceiver station BTS1 in the case shown in FIG. 1. The Base Station Sub-system BSS includes a Base Station Controller BSC and subordinated base transceiver stations BTS. Usually, there are several base station controllers BSC subordinated to a Mobile Services Switching Centre MSC. The mobile services switching centre MSC is connected to other mobile services switching centres, and through a Gateway Mobile Services Switching Centre GMSC the GSM network is connected with other networks, such as a public switched telephone network PSTN, another public land mobile network PLMN or an ISDN network. The operation of the whole system is monitored by an Operation and Maintenance Centre OMC.
The mobile station MS measures the reception level (field strength) and quality of the downlink signal received from the base transceiver station BTS1 of the serving cell, while the base transceiver station BTS1 of the serving cell for its part measures the reception level (field strength) and quality of the uplink signal received from the mobile station MS. Based on these measurement results and on the established power regulation parameters, the power regulation algorithm determines a suitable transmission power level at the base transceiver station and/or in the mobile station. The transmission power level determined for the mobile station is made known to the mobile station MS in a power regulation instruction. Power regulation is carried out constantly during a call, e.g. in a GSM system of the TDMA type typically twice a second, and in a UMTS-WCDMA system (Universal Mobile Telecommunication Systemxe2x80x94Wide band CDMA) of the CDMA type 1600 times a second.
A known power regulation algorithm is C-based power control, wherein the determination of the transmission power is based on the power level C received from the radio communication. In this algorithm, the transmission power is the same for such radio communications which have the same attenuation over the radio path. FIG. 2 shows such a situation as an example, where mobile stations MS1 and MS2 in radio communication with a base transceiver station BTS1 are located at an equal distance attenuation from this serving base transceiver station. In the situation shown in FIG. 2, the signal is transmitted to the mobile stations from the serving base transceiver station BTS1 at equal transmission powers, although they are located in interference fields of different magnitudes, because mobile station MS1 receives more interference than mobile station MS2 from base transceiver station BTS2, which is operating at the same frequency. Thus, the problem with C power regulation is the inefficiency of the power regulation as regards co-channel interference.
Another known power regulation algorithm is C-based power control, wherein the transmission power determination is based on the quality of the signal received from the radio communication, which is measured from the received useful signal. Since the quality of the useful signal is also affected by the interference level of the reception, besides being affected by the received power level, the transmission from base transceiver station BTS1 in the situation shown as an example in FIG. 2 is at a higher transmission power to mobile station MS1 than to mobile station MS2. Hereby, the downlink transmission power is used to compensate for the co-channel interference received by the mobile station from other base transceiver stations. However, the high variation of interference is a problem with C/I power regulation, because C/I power regulation reacts to changes in the interference level with a delay, due to a delay in the signalling of measurement results, among other things. A high variation of interference will have the time to lower before the power regulation is able to compensate for the increase in interference, and also to increase to disturb the radio communication just when the power regulation has time to react to the low interference by reducing the transmission power. Such a variation of interference occurs e.g. in connection with techniques which make interference occur at random, such as frequency hopping and dynamic channel allocation, and/or in connection with packet data transmission.
Thus, the problem with the above-mentioned power regulation algorithms is the interference signals transmitted at the same frequency as the radio communication, especially in connection with co-channel interference occurring with a variation of interference.
It is the purpose of this invention to bring about an efficient power regulation method, especially in an environment where variation of interference occurs.
This objective is achieved with a method in accordance with the invention, which is characterised by that which is said in the independent claims. Special embodiments of the invention are presented in the dependent claims.
The invention is based on the idea that the power regulation decision uses the measurement results of co-channel adjacent transmitter signals, besides the measurement results of the radio communication to be relayed. From the measurement results of the adjacent transmitter signals transmitted at the same frequency and in the same time slot as the monitored radio communication, an estimate is determined of that interference caused to the radio communication which is to be compensated for by regulating the transmission power of the desired signal. The estimate of the interference caused to the radio communication is preferably based on the geographical location of the interference source and on the long-term behavior of the interference power. Hereby the power regulation will react to the average interference value only, not to any individual instantaneous interference value. Thus, in a cellular radio network the power regulation is based on the network""s cell isolation seen from the mobile station""s view-point, that is, on the radio-technical degree of isolation of co-channel cells.
It is an advantage of the power regulation in accordance with the invention that it is efficient and stable in an environment with variable interference and especially in the radio network of irregular cells and/or in a cellular radio network, wherein there, are short frequency reuse distances. The power regulation in accordance with the invention is especially advantageous in a high variance interference field, e.g. when using techniques causing random interference, e.g. frequency hopping, and in packet form transmission.
It is another advantage of the power regulation in accordance with the invention that it does not require any additional traffic or signalling on the transmission path, especially in regard to C/I power regulation.
In addition, it is an advantage of the power regulation in accordance with the invention that it achieves a better C/I distribution in the network than what is achieved with known power regulation techniques.